B-staged, resin rich, electrically insulating tapes have been known for many years. These tapes find one of their greatest uses in large rotating electrical machines or high voltage motors. Typically, these tapes comprise an epoxy resin impregnated mica in the form of flakes, splittings or paper, supported on an electrically insulating scrim. The impregnating resin is then B-staged or partially cross-linked during the manufacturing process. Then, since the material in the B-staged state is manufactured in large sheets, these sheets are slit into desired widths to form the tapes, which may later be used to wrap about an electrical conductor to be insulated and placed in an oven where, under heat or heat and pressure, the resin is cured.
Although these tapes are being used presently, they are not without certain drawbacks. First, manufacturers are constantly trying to develop a tape in which the resin can be B-staged and then remain flexible for long periods of time to extend the shelf life of such tapes. However, the designers of such tapes must not make a tape system which will require long periods of time at temperature and pressure to cure the resin about the substrate, as this will add significant costs to the process.
Second, the physical properties of the cured insulation are important, such as the high flexural strength and low dissipation factors which are necessary to meet the electrical and physical properties required in the industry.
Third, since mica paper based products are not very stable in a moisture bearing environment, a tape having improved moisture resistance would also be desirable.
Therefore, what is needed in the art is a resin rich, electrically insulating tape which is stable in the B-staged condition for good shelf life, yet is rapid curing, while having high flexural strength, low dissipation factor and improved moisture resistance when cured.